This invention relates to the field of retroreflectors, and more particularly to a hollow retroreflector mounted within a receptacle so that the entire assembly defines a hollow surveying retroreflector assembly.
Hollow retroreflectors are old in the art. Hollow retroreflectors are made of three plates joined together having optically flat reflecting faces disposed at right angles to each other, and meeting at what can be described as a common inside corner of an imaginary cube.
Hollow retroreflectors in general have the essential property of causing incident and the reflected light rays to travel along parallel paths. Accordingly, if the reflecting faces of the plates are not disposed at right angles to each other, the hollow retroreflector will not function properly, as it will not be able to deliver the reflected light ray along a path parallel to the incident light ray.
Specific to this invention, surveying retroreflectors are also old in the art. Since the advent of electronic surveying equipment which uses light rays to perform the measuring and calculating functions required in the field of surveying, surveying retroreflectors have been used to receive an incident light ray and reflect that light ray along a parallel path back to its source. Prior art surveying retroreflectors have primarily consisted of solid retroreflectors, as opposed to hollow retroreflectors.
Solid retroreflectors are formed from a glass cube. Three sides of the glass cube are ground until three mutually perpendicular faces are created which radiate from a single point. The three perpendicular faces are then polished and silvered so as to create three reflecting faces at right angles to each other.
A light ray must be able to propagate through the glass of a solid retroreflector in order to be reflected back along a parallel path to the source of the ray. Accordingly, the prior use of solid retroreflectors in surveying retroreflectors inhibit the wave length properties of light rays used in electronic surveying equipment since some wave lengths of light do not propagate well through glass; i.e., far infrared light.
Due to the limited capabilities of solid retroreflectors in the field of surveying, some uses of hollow surveying retroreflectors have been attempted. Unfortunately, the essential requirement of maintaining the reflecting faces of the hollow retroreflector perfectly perpendicular so as to guarantee parallelism of the incident and reflected light rays has not been satisfactorily achieved by the prior art hollow surveying retroreflectors. Prior art hollow surveying retroreflector assemblies have failed to maintain the mutually perpendicular alignment of their reflecting faces whenever they receive a jolt, i.e., as when they are dropped onto the ground, banged into something or simply mishandled.
Accordingly, it would be desirable to provide a hollow surveying retroreflector assembly that does not lose the perpendicular alignment of its reflecting faces, and therefore maintains the parallelism of the incident and reflected light rays which are vital to the proper functioning of a retroreflector.